React.js: Identifying different inputs with one onChange handler

Question

Curious what the right way to approach this is:

var Hello = React.createClass({
getInitialState: function() {
    return {total: 0, input1:0, input2:0};
},
render: function() {
    return (
        <div>{this.state.total}<br/>
            <input type="text" value={this.state.input1} onChange={this.handleChange} />
            <input type="text" value={this.state.input2} onChange={this.handleChange} />
        </div>
    );
},
handleChange: function(e){
    this.setState({ ??? : e.target.value});
    t = this.state.input1 + this.state.input2;
    this.setState({total: t});
}
});

React.renderComponent(<Hello />, document.getElementById('content'));

Obviously you could create separate handleChange functions to handle each different input, but that's not very nice. Similarly you could create a component just for an individual input, but I wanted to see if there's a way to do it like this.

Answer 1

I suggest sticking to standard HTML attributes like name on input Elements to identify your inputs. Also, you don't need to keep "total" as a separate value in state because it is composable by adding other values in your state:

var Hello = React.createClass({
    getInitialState: function() {
        return {input1: 0, input2: 0};
    },
    render: function() {
        const total = this.state.input1 + this.state.input2;

        return (
            <div>{total}<br/>
                <input type="text" value={this.state.input1} name="input1" onChange={this.handleChange} />
                <input type="text" value={this.state.input2} name="input2" onChange={this.handleChange} />
            </div>
        );
    },
    handleChange: function(e) {
        this.setState({[e.target.name]: e.target.value});
    }
});

React.renderComponent(<Hello />, document.getElementById('content'));

Answer 2

You can use the .bind method to pre-build the parameters to the handleChange method. It would be something like:

  var Hello = React.createClass({
    getInitialState: function() {
        return {input1:0, 
                input2:0};
    },
    render: function() {
      var total = this.state.input1 + this.state.input2;
      return (
        <div>{total}<br/>
          <input type="text" value={this.state.input1} 
                             onChange={this.handleChange.bind(this, 'input1')} />
          <input type="text" value={this.state.input2} 
                             onChange={this.handleChange.bind(this, 'input2')} />
        </div>
      );
    },
    handleChange: function (name, e) {
      var change = {};
      change[name] = e.target.value;
      this.setState(change);
    }
  });

  React.renderComponent(<Hello />, document.getElementById('content'));

(I also made total be computed at render time, as it is the recommended thing to do.)

Answer 3

The onChange event bubbles... So you can do something like this:

// A sample form
render () {
  <form onChange={setField}>
    <input name="input1" />
    <input name="input2" />
  </form>
}

And your setField method might look like this (assuming you're using ES2015 or later:

setField (e) {
  this.setState({[e.target.name]: e.target.value})
}

I use something similar to this in several apps, and it's pretty handy.

Answer 4

Deprecated solution

valueLink/checkedLink are deprecated from core React, because it is confusing some users. This answer won't work if you use a recent version of React. But if you like it, you can easily emulate it by creating your own Input component

Old answer content:

What you want to achieve can be much more easily achieved using the 2-way data binding helpers of React.

var Hello = React.createClass({
    mixins: [React.addons.LinkedStateMixin],
    getInitialState: function() {
        return {input1: 0, input2: 0};
    },

    render: function() {
        var total = this.state.input1 + this.state.input2;
        return (
            <div>{total}<br/>
                <input type="text" valueLink={this.linkState('input1')} />;
                <input type="text" valueLink={this.linkState('input2')} />;
            </div>
        );
    }

});

React.renderComponent(<Hello />, document.getElementById('content'));

Easy right?

http://facebook.github.io/react/docs/two-way-binding-helpers.html

You can even implement your own mixin

Answer 5

You can also do it like this:

...
constructor() {
    super();
    this.state = { input1: 0, input2: 0 };
    this.handleChange = this.handleChange.bind(this);
}

handleChange(input, value) {
    this.setState({
        [input]: value
    })
}

render() {
    const total = this.state.input1 + this.state.input2;
    return (
        <div>
            {total}<br />
            <input type="text" onChange={e => this.handleChange('input1', e.target.value)} />
            <input type="text" onChange={e => this.handleChange('input2', e.target.value)} />
        </div>
    )
}

Answer 6

If anyone looking for Functional Component Example,

import React, { useState } from "react";

export default function Exapmle() {

const [userState, setUserState] = useState({
  firstName: "",
  lastName: ""
})

const handleChange = (e)=>{
   const value = e.target.value;
   setUserState({
    ...userState,
    [e.target.name]: value
   });
}

return (
  <form>

    <label>
      First name
      <input type="text" name="firstName" value={userState.firstName}
        onChange={handleChange}
      />
    </label>

    <label>
      Last name
      <input type="text" name="lastName" value={userState.lastName}
        onChange={handleChange}
      />
    </label>

  </form>
 );
}

Answer 7

You can use a special React attribute called ref and then match the real DOM nodes in the onChange event using React's getDOMNode() function:

handleClick: function(event) {
  if (event.target === this.refs.prev.getDOMNode()) {
    ...
  }
}

render: function() {
  ...
  <button ref="prev" onClick={this.handleClick}>Previous question</button>
  <button ref="next" onClick={this.handleClick}>Next question</button>
  ...
}